The present invention relates to an aqueous emulsion containing silicone rubber particles which has a number average particle size of at most 0.1 xcexcm and a narrow particle size distribution, and which is suitable for use in impact modifier, softener, fiber treating agent, hair treating agent, slipping agent, water repellent, processing aid for molding materials, flame retardant, coating material and the like, and also to a process for the preparation of the aqueous emulsion.
Silicone rubbers have good properties such as elasticity, water resistance, thermal stability, weatherability, flame resistance and lubricity and, therefore, aqueous emulsions containing them have been widely used in impact modifier, softener, fiber treating agent, hair treating agent, slipping agent, water repellent, processing aid for molding materials, flame retardant, coating material and the like. In these uses, it is effective in exhibiting higher performances to adjust the number average particle size of the aqueous emulsions of silicone rubber particles to not more than 0.1 xcexcm and to make the particle size distribution of the emulsions narrow. Some proposals to obtain such aqueous emulsions of silicone rubber particles have been made, but satisfactory emulsions have not yet been obtained.
Japanese Patent Publication Kokai No. 62-141029 discloses a process for preparing an aqueous emulsion containing silicone rubber particles having a particle size of at most 0.1 xcexcm which comprises adding an emulsion composed of an organosiloxane, an emulsifier and water to a reaction system containing water and a polymerization catalyst and carrying out the polymerization.
Japanese Patent Publication Kokai No. 5-194740 discloses a process for preparing an aqueous emulsion containing silicone rubber particles having a particle size of at most 0.1 xcexcm which comprises adding dropwise an emulsion composed of a mixture of an organosiloxane, a siloxane-based crosslinking agent and a siloxane-based graftlinking agent, an emulsifier and water to a reaction system containing water and a polymerization catalyst, while carrying out the polymerization.
However, in both processes disclosed in Japanese Patent Publications Kokai No. 62-141029 and Kokai No. 5-194740, at least 13 parts by weight of an emulsifier is required per 100 parts by weight of the silicone rubber in the aqueous silicone rubber emulsion when it is desired to adjust the particle size of the emulsion to not more than 0.1 xcexcm and to make the particle size distribution narrow, for example, to adjust the variation coefficient (standard deviation/average particle size (%)) which is a measure of the particle size distribution to not more than 65%. Thus, in case of using aqueous silicone rubber emulsions obtained by such conventional processes as impact modifier, slipping agent or flame retardant, there arises a problem that molded articles are easy to be colored. Also, in case of using them as coating material or fiber treating agent, there arises a problem that the water repellency is deteriorated.
Thus, it is an object of the present invention to provide an aqueous emulsion of silicone rubber particles having a number average particle size of at most 0.1 xcexcm and a narrow particle size distribution (variation coefficient of at most 65%) which has a small content of an emulsifier.
A further object of the present invention is to provide a process for preparing an aqueous emulsion of silicone rubber particles according to which an aqueous emulsion of silicone rubber particles having a number average particle size of at most 0.1 xcexcm and a narrow particle size distribution can be prepared with use of a small amount of an emulsifier.
Another object of the present invention is to provide an aqueous emulsion containing silicone rubber-based graft copolymer particles, which is prepared from silicone rubber particles having a number average particle size of at most 0.1 xcexcm and a narrow particle size distribution.
Still another object of the present invention is to provide a resin composition wherein such silicone rubber particles and/or graft copolymer particles are incorporated into a thermoplastic resin.
The present inventors have found, as a result of making an intensive study in view of the problems mentioned above, that an aqueous emulsion containing silicone rubber particles having a number average particle size of 0.008 to 0.1 xcexcm and a variation coefficient in particle size distribution of at most 65% is obtained with use of a small amount of an emulsifier, while maintaining properties of conventional aqueous emulsions containing silicone rubber particles, by polymerizing silicone rubber-forming components in an aqueous emulsion of a vinyl polymer or copolymer, and that an aqueous emulsion of silicone rubber-based graft copolymer particles wherein a vinyl polymer is grafted onto silicone rubber-containing polymer particles having a small number average particle size and a small variation coefficient of the particle size distribution is obtained by polymerizing a vinyl monomer in the above-mentioned aqueous emulsion containing silicone rubber particles.
Thus, the present invention provides a silicone rubber particle-containing aqueous emulsion which contains polymer particles comprising (A) 0.1 to 45% by weight of a vinyl homopolymer or copolymer and (B) 55 to 99.9% by weight of a silicone rubber, wherein said polymer particles have a number average particle size of 0.008 to 0.1 xcexcm and a variation coefficient in particle size distribution of at most 65%, and said emulsion contains at most 10 parts by weight of an emulsifier per 100 parts by weight of said silicone rubber (B).
The silicone rubber particle-containing aqueous emulsion is prepared by adding (b) 60 to 99.9 parts by weight of a silicone rubber-forming component comprising 50 to 100% by weight of a mixture of an organosiloxane and a difunctional silane compound, 0 to 50% by weight of a silane compound having a functionality of at least 3 and 0 to 50% by weight of a polymerizable vinyl group-containing silane compound to an aqueous emulsion containing the vinyl homopolymer or copolymer (A) obtained by emulsion-polymerizing (a) 0.1 to 40 parts by weight of at least one vinyl monomer selected from the group consisting of an aromatic vinyl monomer, a vinyl cyanide monomer, a halogen-containing vinyl monomer, a (meth)acrylic ester monomer, a carboxyl group-containing vinyl monomer and a conjugated diene monomer so that the total amount of the vinyl monomer (a) and the silicone rubber-forming component (b) is 100 parts by weight, and polymerizing the silicone rubber-forming component (b). The silicone rubber particles are obtained by coagulating the silicone rubber particle-containing aqueous emulsion followed by dehydration and drying.
The present invention also provides an aqueous emulsion containing silicone rubber-based graft copolymer particles, which is prepared by polymerizing a vinyl monomer (c) in an aqueous emulsion containing the above-mentioned silicone rubber particle-containing aqueous emulsion. The graft copolymer particles are obtained by coagulating the graft copolymer particle-containing aqueous emulsion followed by dehydration and drying.
These aqueous emulsion of silicone rubber and aqueous emulsion of silicone rubber-based graft copolymer have a small average particle size, a narrow particle size distribution and a low content of an emulsifier. Therefore, they efficiently exhibit desirable properties without causing problems owing to an emulsifier and are very useful for various purposes, for example, as impact modifier, softener, fiber treating agent, hair treating agent, slipping agent, water repellent, processing aid for molding materials, flame retardant, coating material, and the like.
Thus, the present invention further provides a thermoplastic resin composition comprising a thermoplastic resin and the silicone rubber particles and/or silicone rubber-based graft copolymer particles as mentioned above. The thermoplastic resin composition of the present invention has excellent properties such as impact resistance, processability, appearance of molded articles, slippability and flame resistance.
The term xe2x80x9cvinylxe2x80x9d as used herein indicates a concept including polymerizable Cxe2x95x90C bonds such as vinyl and vinylidene, and also encompasses Cxe2x95x90C bonds as included in conjugated diene compounds.
The aqueous silicone rubber emulsion of the present invention is an aqueous emulsion containing polymer particles comprising (A) 0.1 to 45% by weight of a vinyl homopolymer or copolymer and (B) 55 to 99.9% by weight of a silicone rubber. The polymer particles comprising the vinyl homopolymer or copolymer and the silicone rubber include, for instance, polymer particles obtained by polymerizing a component capable of forming the silicone rubber (B) (silicone rubber-forming component (b)) in the presence of particles of the vinyl homo- or copolymer (A); polymer particles obtained by polymerizing a component capable of forming the vinyl homo- or copolymer (A) (vinyl monomer (a)) in the presence of particles of the silicone rubber (B); polymer particles obtained by, using an emulsion containing both the vinyl monomer (a) and the silicone rubber-forming component (b), firstly polymerizing either one of the vinyl monomer (a) and the silicone rubber-forming component (b) and then conducting the polymerization of the rest. Of these, preferred are the polymer particles obtained by polymerizing the silicone rubber-forming component (b) in the presence of the vinyl homo- or copolymer particles (A), and the polymer particles obtained by, in an emulsion containing both the vinyl monomer (a) and the silicone rubber-forming component (b), firstly polymerizing the vinyl monomer (a) and then conducting the polymerization of the silicone rubber-forming component (b). In particular, the polymer particles obtained by polymerizing the silicone rubber-forming component (b) in the presence of the vinyl homo- or copolymer particles (A) are preferred from the viewpoint of a good stability of the obtained aqueous emulsion containing the silicone rubber particles, though the reason of good stability is unknown.
It is preferable that the particles of vinyl homo- or copolymer (A) used in the preparation of the polymer particles by the polymerization of the silicone rubber-forming component (b) in the presence of the vinyl homo- or copolymer particles (A) are comprised of a vinyl homo- or copolymer whose toluene-insoluble fraction is from 0 to 90% by weight, especially 0 to 30% by weight, more especially 0% by weight, as measured by immersing in toluene at room temperature for 24 hours and whose solvent-soluble portion has a number average molecular weight of 500 to 5,000,000, especially 1,000 to 1,000,000, in terms of polystyrene, and have a number average particle size of 0.005 to 0.09 xcexcm, especially 0.005 to 0.07 xcexcm, and a variation coefficient in particle size distribution of 10 to 65%, especially 20 to 50%. If the content of the toluene-insoluble portion becomes large, the number average particle size of the obtained aqueous silicone rubber emulsion tends to become large. If the number average molecular weight mentioned above is too small or too large, the number average particle size of the obtained aqueous silicone rubber emulsion tends to become large. Also, particles having a too small number average particle size are themselves difficult to obtain, and if the number average particle size is too large, the number average particle size of the obtained aqueous silicone rubber emulsion tends to exceed 0.1 xcexcm. Further, particles having a too small variation coefficient in particle size distribution are themselves difficult to obtain, and if the variation coefficient is too large, the particle size distribution of the obtained aqueous silicone rubber emulsion tends to wide.
Examples of the monomer used in the preparation of the vinyl homo- or copolymer (A) are, for instance, an aromatic vinyl monomer such as styrene, xcex1-methylstyrene, p-methylstyrene or p-butylstyrene; a vinyl cyanide monomer such as acrylonitrile or methacrylonitrile; a halogenated vinyl monomer such as vinyl chloride, vinylidene chloride or vinylidene fluoride; (meth)acrylic ester monomer such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, glycidyl acrylate, hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, lauryl methacrylate, glycidyl methacrylate or hydroxyethyl methacrylate; a carboxyl group-containing vinyl monomer such as itaconic acid, (meth)acrylic acid, fumaric acid or maleic acid; a conjugated diene monomer such as butadiene, chloroprene or isoprene; and the like. These may be used alone or in admixture thereof. Of these, a monomer containing 20 to 100% by weight, especially 30 to 100% by weight, of any of butyl acrylate, 2-ethylhexyl acrylate, butyl methacrylate, butadiene and acrylonitrile is preferred from the viewpoints that the stability of the obtained aqueous silicone rubber emulsion is high and the particle size thereof is easy to become small. Also, styrene, (meth)acrylic acid and the like are preferred as a comonomer therefor.
Also, a compound having at least two polymerizable vinyl groups in its molecule and/or a polymerizable vinyl group-containing silane compound may be used in an amount of at most 10 parts by weight per 100 parts by weight of the monomer used in the preparation of the vinyl homo- or copolymer.
The compound having at least two polymerizable vinyl groups in its molecule is a crosslinking agent which imparts a crosslinked structure to the vinyl homo- or copolymer (A), and includes, for instance, divinyl benzene, allyl methacrylate, triallyl cyanurate and other known crosslinking agents. Also, the polymerizable vinyl group-containing silane compound serves as a graftlinking agent to provide the side chains and/or molecular ends of the vinyl homo- or copolymer (A) with grafting sites which react with the silicone rubber-forming component (b). As the silane compound are used, for instance, those used in the silicone rubber-forming component (b) as described after in detail. Since the number average particle size of the obtained aqueous silicone rubber emulsion tends to increase if the crosslinking agent and/or the graftlinking agent are used, it is preferable not to use them when a sufficiently small average particle size is desired.
Examples of the vinyl homo- or copolymer (A) are, for instance, polybutyl acrylate, butyl acrylate-styrene copolymer, butyl acrylate-methyl methacrylate copolymer, butyl acrylate-butyl methacrylate copolymer, butyl acrylate-2-ethylhexyl acrylate copolymer, butyl acrylate-methacrylic acid-butyl methacrylate copolymer, polybutyl methacrylate, polystyrene, styrene-acrylonitrile copolymer, styrene- butadiene copolymer, polybutadiene, butadiene-butyl acrylate copolymer, polyvinyl chloride, polyvinylidene fluoride, and the like. The polymer (A) may be crosslinked polymers or may be non-crosslinked polymers, but non-crosslinked polymers are preferred since the particle size of the obtained aqueous silicone rubber emulsion becomes smaller. The term xe2x80x9ccopolymerxe2x80x9d as herein used includes random copolymers, block copolymers, graft copolymers and those prepared by a combination of these polymerization methods and is not particularly limited.
The silicone rubber (B) obtained by polymerizing the silicone rubber-forming component (b) in the presence of the vinyl homo- or copolymer (A) exhibits performances such as softness brought about by silicone. The silicone rubber (B) formed by the polymerization of the silicone rubber-forming component (b) may chemically bond with the vinyl polymer (A) to form a single particle, or may form a single particle in the state of being physically mixed with the vinyl polymer (A). Further, the silicone rubber (B) may form a single particle with the vinyl polymer (A) in the state that a part of the rubber (B) chemically bond with the vinyl polymer (A) and a part of the rubber (B) is physically mixed with the vinyl polymer (A), or the emulsion particles may be a mixture of at least two of the above single particles. Also, the silicone rubber (B) may form a silicone rubber particle independently with a vinyl polymer particle (A) without chemically bonding and being physically mixed with the vinyl polymer (A).
The silicone rubber-forming component (b) is a component for forming the silicone rubber (B) through siloxane bonds from an organosiloxane and optionally a silane compound such as a difunctional silane compound, a silane compound having a functinality of at least 3 or a polymerizable vinyl group-containing silane compound. When the silicone rubber-forming component (b) contains a polyfunctional silane compound having a functionality of at least 3 or a polymerizable vinyl group-containing silane compound, crosslinked silicone rubbers (B) are obtained. Also, when the component (b) contains a polymerizable vinyl group-containing silane compound, it provides a grafting site for vinyl monomer (c) described after.
The organosiloxane and the difunctional silane compound constitute the main backbone of the silicone rubber (B). Examples of the organosiloxane are, for instance, a cyclic siloxane such as hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane or trimethyltriphenylcyclosiloxane, a linear organosiloxane oligomer, and the like. Examples of the difunctional silane compound are, for instance, diethoxydimethylsilane, dimethoxydimethylsilane, diphenyldimethoxysilane, diphenyldiethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldimethoxysilane, 4-aminobutylmethyldimethoxlysilane, 3-chloropropylmethyldimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, heptadecafluorodecylmethyldimethoxysilane, trifluoropropylmethyldimethoxysilane, octadecylmethyldimethoxysilane, and the like. Among these combinations of organosiloxane and difunctional silane compound, octamethylcyclotetrasiloxne and mixtures of at least two cyclic siloxanes are preferred from an economical point of view.
The silane compound having a functionality of at least 3 is used as a component for introducing a crosslinked structure by copolymerizing with the organosiloxane and difunctional silane compound, thereby imparting a rubber elasticity to the silicone rubber (B), namely as a crosslinking agent for the silicone rubber. Examples thereof are, for instance, tetrafunctional and trifunctional alkoxysilane compounds such as tetraethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, ethyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 4-aminobutyltrimethoxysilane, 3-chloropropyltrimethoxysilane, 3-gycidoxypropyltrimethoxysilane, heptadecafluorodecyltrimethoxysilane, trifluoropropyltrimethoxysilane and octadecyltrimethoxysilane, and others. Of these, tetraethoxysilane is preferred from the viewpoint of a high crosslinking efficiency.
The polymerizable vinyl group-containing silane compound is a component for introducing polymerizable vinyl groups into the side chains or molecular chain ends by copolymerizing with the organosiloxane, difunctional silane compound or silane compound having a functionality of at least 3. The polymerizable vinyl group serves as a graft-active point upon chemically bonding with a vinyl homo- or copolymer formed from vinyl monomer (c) mentioned after. Further, since crosslinkages can be formed by causing a radical reaction between the graft-active points through a radical polymerization initiator as described after, the polymerizable vinyl group-containing silane compound can be used as a crosslinking agent.
Examples of the polymerizable vinyl group-containing silane compound are, for instance, a silane comound of the formula (I): 
wherein R1 is hydrogen atom or methyl group, R2 is a monovalent hydrocarbon group having 1 to 6 carbon atoms, X is an alkoxyl group having 1 to 6 carbon atoms, a is 0, 1 or 2, and p is an integer of 1 to 6,
a silane compound of the formula (II): 
wherein R2, X, a and p are as defined above,
a silane compound of the formula (III): 
wherein R2, X, a and p are as defined above,
a silane compound of the formula (IV): 
wherein R2, X, a and p are as defined above, and R3 is a bivalent hydrocarbon group having 1 to 6 carbon atoms,
a silane compound of the formula (V): 
wherein R2, X, a and p are as defined above, and R4 is a bivalent hydrocarbon group having 1 to 18 carbon atoms, and the like.
Examples of the group R2 in the formulas (I) to (V) are, for instance, an alkyl group such as methyl group, ethyl group or propyl group, phenyl group, and the like. Examples of the group X are, for instance, methoxy group, ethoxy group, propoxy group and butoxy group and the like. Examples of the group R3 in the formula (IV) are, for instance, methylene group, ethylene group, propylene group butylene group and the like. Examples of the group R4 in the formula (V) are, for instance, methylene group, ethylene group, propylene group butylene group and the like.
Examples of the silane compound (I) are, for instance, xcex2-methacryloyloxyethyldimethoxymethylsilane, xcex3-methacryloyloxypropyldimethoxymethylsilane, xcex3-methacryloyloxypropyltrimethoxysilane, xcex3-methacryloyloxypropyldimethylmethoxysilane, xcex3-methacryloyloxypropyltriethoxysilane, xcex3-methacryloyloxypropyldiethoxymethylsilane, xcex3-methacryloyloxypropyltripropoxysilane, xcex3-methacryloyloxypropyldipropoxymethylsilane, xcex3-acryloyloxypropyltrimethoxysilane, and the like. Examples of the silane compound (II) are, for instance, p-vinylphenyldimethoxymethylsilane, p-vinylphenyltrimethoxysilane, p-vinylphenyltriethoxysilane, p-vinylphenyldiethoxymethylsilane, and the like. Examples of the silane compound (III) are, for instance, vinylmethyldimethoxysilane, vinylmethyldiethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, and the like. Examples of the silane compound (IV) are, for instance, allylmethyldimethoxysilane, allylmethyldiethoxysilane, allyltrimethoxysilane, allyltriethoxysilane, and the like. Examples of the silane compound (V) are, for instance, mercaptopropyltrimethoxysilane, mercaptopropyldimethoxymethylsilane, and the like. Of these, silane compounds of the formulas (I), (II) and (V) are preferably used from the viewpoints of economy and high reactivity.
In case that the above-mentioned polymerizable vinyl group-containing silane compounds are of trialkoxysilane type, they also serve as a crosslinking agent.
With respect to the proportions of the organosiloxane, the difunctional silane compound, the silane compound having a functionality of at least 3 and the polymerizable vinyl group-containing silane compound in the silicone rubber-forming component (b) in the polymerization thereof, it is preferable that the proportion of the total of the organosiloxane and the difunctional silane compound is from 50 to 100% by weight, especially 70 to 100% by weight, more especially 90 to 100% by weight, wherein the ratio of the organosiloxane to the difunctional silane compound is from 100/0 to 50/50 by weight, especially 100/0 to 70/30 by weight, the proportion of the silane compound having a functionality of at least 3 is from 0 to 50% by weight, especially 0 to 30% by weight, more especially 0 to 10% by weight, and the proportion of the the polymerizable vinyl group-containing silane compound is from 0 to 50% by weight, especially 0 to 30% by weight, more especially 0 to 10% by weight.
If the proportion of the total of organosiloxane and difunctional silane compound is less than 50% by weight, the obtained silicone rubber (B) tends to exhibit the properties such as softness with difficulty. The silane compound having a functionality of at least 3 and the polymerizable vinyl group-containing silane compound are optional components. If the proportion of each of these components exceeds 50% by weight, the properties of the silicone rubber are hard to be exhibited. For obtaining effects produced by the use of the silane compound having a functionality of at least 3 or the polymerizable vinyl group-containing silane compound, it is desirable to use each of them in an amount of at least 0.5% by weight.
It is preferable that the toluene-insoluble fraction of polymer particles obtained by polymerizing the silicone rubber-forming component (b) in the presence of particles of the vinyl homo- or copolymer (A) as measured by immersing the polymer particles in toluene for 24 hours is from 0 to 95% by weight, especially from 0 to 90% by weight. If the toluene-insoluble fraction is too large, properties as a rubber tend to be exhibited with difficulty.
The polymer particles obtained by preparing an emulsion containing both the vinyl monomer (a) and the silicone rubber-forming component (b), firstly polymerizing the vinyl monomer (a) and then polymerizing the silicone rubber-forming component (b) tend to have a larger particle size than the above-mentioned polymer particles obtained by adding the component (b) to and polymerizing it in an emulsion of the vinyl polymer (A). The same vinyl monomers as those used in the preparation of the vinyl homo- or copolymer (A) can be used as the vinyl monomer (a) in this method. Also, the proportions of the vinyl monomer (a) and the respective components of the silicone rubber-forming component (b) are the same as in the above-mentioned preparation of the polymer particles by polymerizing the silicone rubber-forming component (b) in the presence of the particles of vinyl homo- or copolymer (A).
It is preferable that the toluene-insoluble fraction of polymer particles obtained by preparing an emulsion containing both the vinyl monomer (a) and the silicone rubber-forming component (b), firstly polymerizing the vinyl monomer (a) and then polymerizing the silicone rubber-forming component (b), as measured by immersing the polymer particles in toluene for 24 hours is from 0 to 95% by weight, especially from 0 to 90% by weight. If the toluene-insoluble fraction is too large, properties as a rubber tend to be exhibited with difficulty.
The proportions of polymer components in the particles of the aqueous silicone rubber particle-containing emulsion of the present invention are from 0.1 to 45% by weight, preferably 0.6 to 35% by weight, more preferably 1 to 12% by weight, for the vinyl homo- or copolymer (A), and from 55 to 99.9% by weight, preferably 65 to 99.4% by weight, more preferably 88 to 99% by weight, for the silicone rubber (B). If the proportion of the vinyl homo- or copolymer (A) in the particles is less than 0.1% by weight, namely if the proportion of the silicone rubber (B) is more than 99.9% by weight, the particle size of the aqueous silicone rubber particle-containing emulsion tends to become large. If the proportion of the vinyl homo- or copolymer (A) in the particles is more than 45% by weight, namely if the proportion of the silicone rubber (B) is less than 55% by weight, the properties of silicone rubber tend to be exhibited with difficulty.
The number average particle size of the aqueous silicone rubber particle-containing emulsion of the present invention is from 0.008 to 0.1 xcexcm, preferably 0.008 to 0.06 xcexcm, more preferably 0.008 to 0.04 xcexcm. It is difficult to obtain an emulsion having a number average particle size of less than 0.008 xcexcm, and if the number average particle size is more than 0.1 xcexcm, an impact resistance-imparting effect as expected when used as an impact modifier tends to be lowered.
Also, the variation coefficient in particle size distribution of the number average particle size is from 10 to 65%, preferably 20 to 55%, more preferably 20 to 50%. It is difficult to obtain the particles having a variation coefficient of less than 10%. If the variation coefficient is more than 65%, an impact resistance-imparting effect as expected when used as an impact modifier tends to be lowered.
The amount of an emulsifier included in the aqueous silicone rubber particle-containing emulsion of the present invention is at most 10 parts by weight, preferably from 0.5 to 8 parts by weight, more preferably from 1.5 to 6 parts by weight, per 100 parts by weight of the silicone rubber (B). If the amount of the emulsifier is more than 10 parts by weight, the appearance of resins is deteriorated, for example, when the emulsion is used as an impact modifier or slipping agent for thermoplastic resins. If the amount of the emulsifier is less than 0.5 part by weight, the stability of the emulsion tends to be decreased.
Preferably, the solid content of the aqueous silicone rubber particle-containing emulsion of the present invention is from 10 to 50% by weight, especially 15 to 40% by weight. If the solid content is less than 10% by weight, a large amount of the emulsion must be used, for example, when used as an impact modifier, since the concentration of the effective component is small, thus the productivity is lowered. If the solid content is more than 50% by weight, the stability of the emulsion tends to be decreased.
An explanation is given below with respect to a process for preparing the aqueous silicone rubber particle-containing emulsion of the present invention.
The preparation of the aqueous emulsion containing the polymer particles obtained by polymerizing silicone rubber-forming component (b) in the presence of the particles of vinyl homo- or copolymer (A) is carried out, for example, in the following manner.
Preferably, to an aqueous emulsion of vinyl homo- or copolymer (A) obtained by emulsion-polymerizing 0.1 to 40 parts by weight, especially 0.5 to 30 parts by weight, more especially 1 to 10 parts by weight, of at least one member selected, as a component for preparing the vinyl homo- or copolymer (A) (vinyl monomer (a)), from the group consisting of an aromatic vinyl monomer, a vinyl cyanide monomer, a halogenated vinyl monomer, a (meth)acrylic ester monomer, a carboxyl group-containing vinyl monomer and a conjugated diene monomer, there is added an aqueous emulsion containing 60 to 99.9 parts by weight, especially 80 to 99.5% by weight, more especially 90 to 99% by weight, of a silicone rubber-forming component (b) comprising 50 to 100% by weight, especially 70 to 100% by weight, more especially 90 to 100% by weight, of the total of an organosiloxane and a difunctional silane compound, 0 to 50% by weight, especially 0 to 30% by weight, more especially 0 to 10% by weight, of a silane compound having a functionality of at least 3, and 0 to 50% by weight, especially 0 to 30% by weight, more especially 0 to 10% by weight, of a polymeriable vinyl group-containing silane compound, so that the total amount of the components (a) and (b) becomes 100 parts by weight, followed by the polymerization of the component (b) to form a silicone rubber (B).
The aqueous emulsion of the vinyl homo- or copolymer (A) is obtained by polymerizing the vinyl monomer (a) by a usual emulsion polymrization method, for example, by a method as disclosed in Japanese Patent Publication Kokai No. 50-88169 or No. 61-1417469.
The number average particle size of the aqueous emulsion of the vinyl homo- or copolymer (A) is preferably, as described above, from 0.005 to 0.09 xcexcm, especially 0.005 to 0.07 xcexcm, and the variation coefficient in the particle size distribution is preferably from 10 to 65%, especially 20 to 50%.
The emulsion having a particle size within the range as mentioned above is readily obtained by adjusting the amount of an emulsifier used in the emulsion polymerization of the vinyl monomer (a) (hereinafter referred to as xe2x80x9cemulsifier (xcex1)xe2x80x9d).
Preferably, the amount of the emulsifier (xcex1) is from 0.001 to 7.95 parts by weight, especially 0.01 to 7 parts by weight, more especially 0.1 to 5 parts by weight, per 100 parts by weight of the silicone rubber-forming component (b). If the amount is less than 0.001 part by weight, the number average particle size of the aqueous emulsion of vinyl homo- or copolymer (A) becomes larger than 0.09 xcexcm, and the number average particle size of the obtained aqueus silicone rubber emulsion tends to exceed 0.1 xcexcm. On the other hand, if the amount is more than 7.95 parts by weight, the total amount of the emulsifier (xcex1) and an emulsifier used in the polymerization of the silicone rubber-forming component (b) will exceed 8 parts by weight. Thus, since the polymerization conversion of the silicone rubber-forming component (b) is usually 80% by weight or more, the amount of the emulsifier in the aqueous silicone rubber particle-containing emulsion will become 10 parts by weight or more per 100 parts by weight of the silicone rubber, so the appearance of resins tends to be deteriorated when used, for example, as an impact modifier.
Preferably, the amount of the emulsifier (xcex1) is also from 0.0015 to 7950 parts by weight, especially 0.015 to 7000 parts by weight, per 100 parts by weight of the vinyl monomer (a). If the amount is less than 0.0015 part by weight, the number average particle size of the aqueous silicone rubber particle-containing emulsion tends to exceed 0.1 xcexcm, and if the amount is more than 7950 parts by weight, the appearance of resins tends to be deteriorated when used, for example, as an impact modifier.
Emulsifiers which have been used in usual emulsion polymerization are used as the emulsifier (xcex1) without any particular restriction. Examples of the emulsifier (xcex1) are, for instance, an anionic surfactant such as sodium oleate, potassium oleate, sodium palmitate, potassium palmitate, sodium salt of rosin, potassium salt of rosin, alkylbenzenesulfonic acid, sodium alkylbenzenesulfonate, alkylsulfonic acid, sodium alkylsulfonate, sodium (di)alkyl sulfosuccinate, sodium polyoxyethylene nonylphenyl ether sulfonate or sodium alkylsulfate; a non-ionic surfactant such as polyoxyethylene nonylphenyl ether or polyoxyethylene lauryl ether; a cationic surfactant such as benzylmethyldodecyl ammonium hydroxide, octyltrimethyl ammonium chloride, dodecyltrimethyl ammonium chloride or hexadecyltrimethyl ammonium chloride; and the like. The emulsifiers may be used alone or in admixture thereof. From the viewpoint of a high stability of emulsion, preferred are sodium alkylbenzenesulfonate, sodium alkylsulfonate, sodium (di)alkyl sulfosuccinate, sodium alkylsulfate and benzylmethyldodecyl ammonium hydroxide.
Also, the amount of the vinyl monomer (a) is from 0.1 to 40 parts by weight, especially 0.5 to 30 parts by weight, more especially 1 to 10 parts by weight, based on 100 parts by weight of the total of the vinyl monomer (a) and the silicone rubber-forming component (b). If the amount of the vinyl monomer (a) is less than 0.1 part by weight, the particle size of the obtained aqueous silicone rubber emulsion tends to become large, and if the amount is more than 40 parts by weight, the polymerization conversion of the silicone rubber-forming component (b) tends to decrease.
The radical reaction in the polymerization can be conducted without particular restriction so long as usual radical polymerization is adopted, e.g., a method wherein a polymerization is proceeded by thermally decomposing a radical initiator, or a redox polymerization using a reducing agent.
Examples of the radical initiator are an organic peroxide such as cumene hydroperoxide, tert-butyl hydroperoxide, benzoyl peroxide, tert-butylperoxy isopropylcarbonate, di-tert-butyl peroxide, tert-butylperoxy laurate or lauroyl peroxide; an inorganic peroxide such as potassium persulfate or ammonium persulfate; an azo compound such as 2,2xe2x80x2-azobisisobutylonitrile or 2,2xe2x80x2-azobis-2,4-dimethylvaleronitrile; and the like. Of these, organic peroxides and inorganic peroxides are preferably used from the viewpoint of a high reactivity.
Examples of the reducing agent used in the redox system are a mixture of ferrous sulfate/glucose/sodium pyrophosphate, a mixture of ferrous sulfate/dextrose/sodium pyrophosphate, a mixture of ferrous sulfate/sodium formaldehyde sulfoxylate/ethylenediamineacetate, and the like.
The radical polymerization initiator is used usually in an amount of 0.005 to 20 parts by weight, especially 0.01 to 10 parts by weight, more especially 0.03 to 5 parts by weight, per 100 parts by weight of the vinyl monomer (a) used. If the amount of the initiator is less than 0.005 part by weight, the polymerization velocity is low, so the production efficiency tends to be lowered, and if the amount is more than 20 parts by weight, heat generation during the polymerization becomes large, so the production tends to become difficult.
A chain transfer agent may also be used upon the radical reaction, as occasion demands. The chain transfer agent is not particularly limited, and any of chain transfer agents used in a usual emulsion polymerization can be used. Examples of the chain transfer agent are, for instance, t-dodecylmercaptan, n-octylmercaptan, n-tetradecylmercaptan, n-hexylmercaptan, and the like. The amount of the chain transfer agent is preferable from 0.01 to 5 parts by weight per 100 parts by weight of the vinyl monomer (a). If the amount is less than 0.01 part by weight, no effect of the use thereof is obtained, and if the amount is more than 5 parts by weight, the polymerization velocity tends to decrease, so the production efficiency is lowered.
Preferably, the reaction temperature in the polymerization of the vinyl monomer (a) is from 30 to 120xc2x0 C.
Preferably, pH of the polymerization system is from 1.2 to 12, especially 2 to 11. If the pH is less than 1.2 or more than 12, when (meth)acrylic ester monomers are used as the vinyl monomer (a), the ester bonds in the side chains thereof are easy to be hydrolyzed during the polymerization.
Preferably, the thus obtained aqueous emulsion of vinyl homo- or copolymer (A) has a solid concentration of 0.1 to 50% by weight, especially 0.5 to 40% by weight. If the solid concentration is less than 0.1% by weight, the particle size of the obtained aqueous silicone rubber particle-containing emulsion tends to become large. If the solid concentration is more than 50% by weight, the stability of the emulsion tends to be lowered.
The aqueous silicone rubber particle-containing emulsion can be obtained by adding an emulsion of silicone rubber-forming component (b) to the aqueous emulsion of vinyl homo- or copolymer (A) and polymerizing the silicone rubber-forming component (b) under an acidic or basic condition to form silicone rubber (B). In particular, from the viewpoint that the particle size of the obtained silicone rubber particle-containing aqueous emulsion is easy to become small, it is preferable to polymerize the component (b) under an acidic condition.
The polymerization of the silicone rubber-forming component (b) in the emulsion state can be carried out by mixing the silicone rubber-forming component (b), an emulsifier (hereinafter referred to as xe2x80x9cemulsifier (xcex2)xe2x80x9d) and water, applying a mechanical shearing force to the resulting mixture to prepare an emulsion, adding the resulting emulsion to the above-mentioned aqueous emulsion of vinyl homo- or copolymer (A) and heating the mixed emulsion at a temperature of not less than 60xc2x0 C. under an acidic or basic condition.
Of the compounds included in the silicone rubber-forming component (b), an organosiloxane and a difunctinal silane compound may be firstly polymerized to form an aqueous emulsion containing silicone rubber particles and, thereafter, a silane compound having a functionality of at least 3 and/or a polymerizable vinyl group-containing silane compound may be added thereto as they are or in the form of an emulsion in amounts within the ranges mentioned above under an acidic or basic condition, followed by polymerization thereof. The addition of the polymerizable vinyl group-containing silane compound in such a manner is preferable, since the polymerizable vinyl group is prevented from being deactivated by heating in the polymerization for producing the silicone rubber (B).
As the emulsifier (xcex2), in general, aninonic and non-ionic surfactants which do not lose an emulsifying ability under an acidic condition are used under an acidic condition, and cationic surfactants are used under a basic condition. Examples of the anionic surfactant are, for instance, alkylbenzenesulfonic acid, sodium alkylbenzenesulfonate, alkylsulfonic acid, sodium alkylsulfonate, sodium (di)alkyl sulfosuccinate, sodium polyoxyethylene nonylphenyl ether sulfonate, sodium alkylsulfate, and the like. These may be used alone or in admixture thereof. Examples of the non-ionic surfactant are, for instance, polyoxyethylene nonylphenyl ether, polyoxyethylene lauryl ether, and the like. The non-ionic surfactants may be used alone or in admixture thereof or may be used in combination with anionic surfactants. Examples of the cationic surfactant are, for instance, benzylmethyldodecyl ammonium hydroxide, octyltrimethyl ammonium chloride, dodecyltrimethyl ammonium chloride, hexadecyltrimethyl ammonium chloride, and the like. These may be used alone or in admixture thereof. Among the above, from the viewpoint of a relatively high effect of stabilizing emulsion, preferred are alkylbenzenesulfonic acid, sodium alkylbenzenesulfonate, alkylsulfonic acid, sodium alkylsulfonate, sodium (di)alkyl sulfosuccinate, and benzylmethyldodecyl ammonium hydroxide. Further, alkylbenzenesulfonic acid, alkylsulfonic acid and benzylmethyldodecyl ammonium hydroxide are particularly preferred since they also serves as a polymerization catalyst for the silicone rubber-forming component. The emulsifier (xcex2) may be the same as or different from the emulsifier (xcex1).
Preferably, the amount of the emulsifier (xcex2) is at least 0.05 part by weight, especially at least 0.1 part by weight, per 100 parts by weight of the total of the vinyl monomer (a) and the silicone rubber-forming component (b), but is adjusted so that the total amount with the emulsifier (xcex1) is at most 8 parts by weight, preferably at most 7 parts by weight, more preferably at most 6 parts by weight, per 100 parts by weight of the silicone rubber-forming component (b). If the amount of the emulsifier (xcex2) is less than 0.05 part by weight, the silicone rubber-forming component (b) is easy to cause phase separation, so the polymerization velocity of the component (b) tends to be lowered. If the total amount of the emulsifiers (xcex1) and (xcex2) exceeds 8 parts by weight, the appearance of thermoplastic resins tends to be deteriorated when the product is used, for example, as an impact modifier or a slipping agent for the resins.
Also, it is preferable that the total amount of the emulsifiers (xcex1) and (xcex2) is from 0.5 to 8 parts by weight, especially 1.5 to 7 parts by weight, per 100 parts by weight of the total of the vinyl monomer (a) and the silicone rubber-forming component (b). If the total amount is less than 0.5 part by weight, the stability of the aqueous silicone rubber particle-containing emulsion tends to be lowered, and if the total amount is more than 8 parts by weight, the appearance of thermoplastic resins tends to be deteriorated when the product is used, for example, as an impact modifier for the resins, or the water repellency is deteriorated when used as a fiber treating agent or a coating material.
The polymerization conversion in the preparation of the vinyl homo- or copolymer (A) from the vinyl monomer (a) is usually at least 95% by weight, and the polymerization conversion in the polymerization of the silicone rubber-forming component (b) in the presence of the vinyl homo- or copolymer (A) from the vinyl monomer (a) is usually at least 80% by weight. Therefore, in order to control the amount of emulsifiers included in the final emulsion to 10 parts by weight or less per 100 parts by weight of the silicone rubber (B), it is preferable to use the emulsifiers so that the total amount of the emulsifiers used, namely total amount of the emulsifiers (xcex1) and (xcex2), is at most 10 parts by weight, especially at most 8 parts by weight, more especially at most 6 parts by weight, per 100 parts by weight of the total of (amount of vinyl monomer (a))xc3x9795% by weight and (amount of silicone rubber-forming component (b))xc3x9780% by weight. The lower limit of the total amount of the emulsifiers is 0.6 part by weight from the viewpoints of controlling the number average particle size of the silicone rubber emulsion to at most 0.1 xcexcm and maintaining the emulsion stable.
Preferably, from the viewpoint of handling of the obtained aqueous silicone rubber particle-containing emulsion, water is used in such an amount that the solid concentration of the falls within the range of 10 to 50% by weight.
Preferably, the preparation of the emulsion of silicone rubber-forming component (b) is carried out by stirring a mixture of component (b), emulsifier (xcex2) and water with a high speed agitator such as a homomixer or a special dispersing machine such as a high pressure homogenizer or a ultrasonic dispersing machine so that the average liquid droplet size becomes 100 xcexcm or less, since the polymerization proceeds at an adequate rate.
The emulsion of the silicone rubber-forming component (b) can be added at once to an aqueous emulsion of the vinyl polymer (A). However, since a narrower particle size distribution is achieved, it is preferable to divide the emulsion of the component (b) into two or more portions and add them, or to add dropwise the emulsion of the component (b) so that the rate of the addition of the component (b) is at most 40 parts by weight per hour based on 100 parts by weight of the total of the vinyl polymer (A) and the component (b).
In case of adding the emulsion at once, the polymerization system can be made acidic or basic in either stage of before or after the addition of the emulsion of the silicone rubber-forming component (b). However, in case of the intermittent addition or the dropwise addition, it is preferable to make the system acidic or basic before the addition.
The acidic condition is adjusted by adding an inorganic acid such as sulfuric acid or hydrochloric acid or an organic acid such as alkylsulfonic acid, alkylbenzenesulfonic acid or trifluoroacetic acid to the system. The pH of the system is preferably from 1.0 to 3, especially 1.2 to 2.5. If the pH is less than 1.0, when the vinyl polymer (A) is (meth)acrylic ester polymers, the ester bonds in the side chains thereof are easy to be hydrolyzed, and if the pH is more than 3, the rate of the polymerization of silicone rubber-forming component (b) tends to be lowered.
When an alkylsulfonic acid or an alkylbenzenesulfonic acid has been used as the emulsifier (xcex1), it is possible to decrease the amount of an acid to be added.
The basic condition is adjusted by adding an inorganic base such as sodium hydroxide, potassium hydroxide or ammonia, or an organic base such as pyridine or benzylmethyldodecyl ammonium hydroxide to the system. The pH of the system is preferably from 11 13.5, especially 11.5 to 13. If the pH is less than 11.0, the polymerization velocity of the silicone rubber-forming component (b) tends to be lowered. If the pH is more than 13, when the vinyl polymer (A) is (meth)acrylic ester polymers, the ester bonds in the side chains thereof are easy to be hydrolyzed.
When benzylmethyldodecyl ammonium hydroxide has been used as the emulsifier (xcex1), it is possible to decrease the amount of a base to be added.
Preferably, the polymerization of the silicone rubber-forming component (b) is carried out at a temperature of 60 to 120xc2x0 C., especially 70 to 100xc2x0 C., since the polymerization velocity is adequate.
The thus obtained aqueous emulsion containing silicone rubber particles is preferably nuetralized, in order to raise the storage stability, by the addition of a basic aqueous solution such as sodium hydroxide or potassium hydroxide when the polymerization has been conducted under an acidic condition, or an acid aqueous solution such as sulfuric acid or hydrochloric acid when the polymerization has been conducted under a basic condition. Before the neutralization, in other words, under the acidic or basic condition, the Sixe2x80x94Oxe2x80x94Si bond which constitutes the silicone rubber backbone is in an equilibrium state between severance and formation, and this equilibrium varies depending on the temperature. The equilibrium shifts to the formation side as the temperature lowers and, therefore, a silicone rubber having a high molecular weight or a high degree of crosslinking is easy to be produced. Thus, when it is desired to obtain a silicone rubber having a high molecular weight or a high degree of crosslinking, it is preferable, after conducting the polymerization at a temperature of 60xc2x0 C. or higher, that the reaction mixture is cooled to about room temperature, maintained at that temperature for 5 to 100 hours and then neutralized.
The preparation of an aqueous emulsion containing polymer particles obtained by preparing an emulsion containing both a vinyl monomer (a) and a silicone rubber-forming component (b), firstly polymerizing the vinyl monomer (a) and then polymerizing the component (b) can be carried out, for example, in the following manner.
Firstly, the vinyl monomer (a) and the silicone rubber-forming component (b) are mixed to prepare a mixture thereof. To the mixture is added a radical polymerization initiator, and it is mixed with an emulsifier and water and applied with mechanical shear to prepare an emulsion. The emulsion is subjected to a polymerization of the vinyl monomer (a) and is then made acidic or basic to polymerize the silicone rubber-forming component, thus the aqueous emulsion containing silicone rubber particles can be obtained.
As the vinyl monomer (a), the silicone rubber-forming component (b) and the radical polymerization initiator can be used those used in the above-mentioned process of the preparation of polymer particles by polymerizing the component (b) in the presence of the particles of vinyl polymer (A). The amounts of the respective components may also be the same.
The above-mentioned emulsifier (xcex2) is used as the emulsifier in this process. It is preferable that the amount of the emulsifier is from 0.5 to 8 parts by weight, especially 1.5 to 7 parts by weight, per 100 parts by weight of the total of the vinyl monomer (a) and the silicone rubber-forming component (b). If the amount is less than 0.5 part by weight, the stability of the aqueous silicone rubber emulsion tends to be lowered. If the amount exceeds 8 parts by weight, the appearance of thermoplastic resins tends to be deteriorated when the product is used, for example, as an impact modifier or a slipping agent for the resins, or the water repellency tends to be deteriorated when used as a fiber treating agent or a coating material.
The preparation of an emulsion by mechanical shearing can be conducted by the same method under the same condition as those in the above-mentioned preparation of the emulsion of silicone rubber-forming component (b).
The polymerization of each of the vinyl monomer (a) and the silicone rubber-forming component (b) can be conducted under the conditions as applied to the above-mentioned preparation of polymer particles by polymerizing the component (b) in the presence of the particles of vinyl polymer (A).
The thus obtained aqueous emulsion containing silicone rubber particles tends to have a larger number average particle size within the range of 0.01 to 0.1 xcexcm, though the particle size distribution thereof is not different from that of the aqueous emulsion containing silicone rubber particles obtained by polymerizing the component (b) in the presence of the particles of vinyl polymer (A).
The aqueous silicone rubber particle-containing emulsions of the present invention obtained by the procedures as mentioned above are suitably employed in uses such as impact modifier, fiber treating agent, slipping agent, water repellent, processing aid for molding materials, flame retardant, coating material and the like.
Aqueous emulsions containing silicone rubber-based graft copolymer particles (which are also referred to as xe2x80x9cgraft copolymer particlesxe2x80x9d hereinafter) according to the present invention can be prepared by polymerizing a vinyl monomer (c) in the presence of the aqueous silicone rubber particle-containing emulsion.
The graft copolymer particles have a structure that a polymer of the vinyl monomer (c) is grafted onto the polymer particles comprising the vinyl polymer (A) and the silicone rubber (B). Preferred are the graft copolymer particles having a number average particle size of at least 0.008 xcexcm, especially at least 0.01 xcexcm, and of at most 0.3 xcexcm, especially at most 0.1 xcexcm. The graft copolymer particles having a number average particle size of less than 0.008 xcexcm is hard to prepare. If the number average particle size is more than 0.3 xcexcm, the properties of silicone rubber tend to be difficult to exhibit.
The content of insoluble matter in the graft copolymer particles as measured by immersing the particles in toluene at room temperature for 24 hours is preferably at least 10% by weight, especially at least 50% by weight. If the content of toluene-insoluble matter is less than 10% by weight, the proportion of a non-grafted polymer of the vinyl monomer (c) increases, so lowering of various physical properties tends to be brought, for example, when the particles are used as impact modifier, fiber treating agent, coating material or the like.
The vinyl monomer (c) is used, for example, to raise the compatibility between silicone rubber-containing polymer particles and a thermoplastic resin so as to uniformly disperse the particles into the thermoplastic resin for the purpose of improving the impact resistance of the thermoplastic resin, or to improve the adhesion with fibers as required when used as a fiber treating agent, or improve the film-forming property as required when used as a coating material.
Preferably, the ratio of the vinyl monomer (c) to the polymer particles included in the above-mentioned aqueous silicone rubber particle-containing emulsion is from 5/95 to 95/5 by weight, especially from 10/90 to 90/10 by weight. If the proportion of the vinyl monomer (c) is too large, for example, a sufficient impact resistance tends to be not exhibited when used as an impact modifier because the content of the silicone rubber (B) is too low, or properties such as water repellency tend to be lowered when used as a fiber treating agent, or the film-forming property tends to be deteriorated when used as a coating material. If the proportion of the vinyl monomer (c) is too small, properties such as compatibility with thermoplastic resins, adhesion with fibers and film strength are not sufficiently improved.
Radical polymerization initiators used in the graft polymerization may be those used in the polymerization of vinyl monomer (a), and the amount thereof may be the same as in the polymerization of vinyl monomer (a). Also, in case of using them in combination with reducing agents, those used in the polymerization of vinyl monomer (a) may be used. In case of using chain transfer agents, too, those used in the polymerization of vinyl monomer (a) may be used, and the amount thereof may be the same.
The polymerization of the vinyl monomer (c) in the presence of the aqueous silicone rubber particle-containing emulsion can be carried out by a usual seed emulsion polymerization method. In particular, it is preferable to carry out the polymerization with adding dropwise a liquid mixture of a vinyl monomer (c) and a radical polymerization initiator. Also, the vinyl monomer (c) may be polymerized in one stage or in multistage.
In the above polymerization, if the silicone rubber (B) contains polymerizable vinyl groups, the vinyl monomer (c) reacts with the polymerizable vinyl groups of the silicone rubber (B) to form grafts upon the polymerization of the vinyl monomer (c) through a radical polymerization initiator. If the vinyl homo- or copolymer (A) is crosslinked, the vinyl monomer (c) also reacts with one of polymerizable vinyl groups, which remains unreacted, of a monomer having at least two polymerizable vinyl groups used as a crosslinking agent, to form grafts. In case that neither the silicone rubber (B) nor the vinyl polymer (A) have a polymerizable vinyl group, if a specific radical polymerization initiator such as t-butyl peroxylaurate is used, it abstracts a hydrogen from an organic group such as methyl group bonded to silicon atom and the vinyl monomer (c) polymerizes to the resulting radicals to form grafts.
Also, if a vinyl monomer (c) containing 0.1 to 30% by weight, preferably 0.5 to 20% by weight, of a polymerizable vinyl group-containing silane compound is polymerized and subjected to a redistribution reaction under an acidic condition of not more than pH 5 or a basic condition of not less than pH 11, grafts are formed. The reason is that the Sixe2x80x94Oxe2x80x94Si bond in the main backbone of the silicone is in an equilibrium state of severance and formation under the acidic or basic condition and, therefore, if a vinyl monomer and a polymerizable vinyl group-containing silane compound are copolymerized in this equilibrium state, the silane present as the side chain of a vinyl copolymer which has been produced by the polymerization or is in the course of production, reacts with the silicone chain to form a graft. If the amount of the polymerizable vinyl group-containing silane compound is less than 0.1% by weight, the proportion of grafting of the vinyl monomer (c) is lowered, so the toluene-insoluble matter content of the graft copolymer particles tends to be decreased, and if the amount is more than 30% by weight, the stability of emulsion tends to be lowered.
From the viewpoint of raising the toluene-insoluble matter content of the graft copolymer particles, it is preferable to prepare the graft copolymer particles by utilizing the redistribution reaction.
Thus, aqueous emulsions containing silicone rubber-based graft copolymer particles wherein the vinyl monomer (c) is graft-polymerized onto the silicone rubber particles as mentioned above are obtained. Such aqueous emulsions are suitably used as impact modifier, slipping agent, fiber treating agent, coating material and the like.
In the polymerization of vinyl monomer (c) in the presence of the aqueous silicone rubber emulsion, the vinyl monomer (c) polymerizes alone without a portion corresponding to the graft of the graft copolymer (namely a polymer of the vinyl monomer (c)) being grafted onto the backbone (namely polymer particles comprising vinyl polymer (A) and silicone rubber (B)) to by-produce so-called free polymer. Thus, the graft polymerization product is obtained in the form of a mixture of a graft copolymer and a free polymer. The term xe2x80x9cgraft copolymerxe2x80x9d as used herein comprehends such a mixture of a graft copolymer and a free polymer.
Recovery of a polymer powder from the aqueous silicone rubber emulsion and the aqueous graft copolymer emulsion as obtained above is carried out by a conventional method, for example, by adding to the aqueous emulsion a metal salt such as calcium chloride, magnesium chloride or magnesium sulfate or an inorganic or organic acid such as hydrochloric acid, sulfuric acid, phosphoric acid or acetic acid to coagulate the aqueous emulsion, followed by dehydration and drying of the deposited polymer. A spray drying method is also applicable.
The powder of these silicone rubber and graft copolymer can be utilized as impact modifier, slipping agent, water repellent, processing aid for molding materials, flame retardant and the like.
The thus obtained silicone rubber particles and graft copolymer particles are incorporated into various thermoplastic resins to give thermoplastic resin compositions having improved impact resistace, processability, slippability and flame resistance.
Examples of the thermoplastic resin are, for instance, polyvinyl chloride, polystyrene, styrene-acrylonitrile copolymer, styrene-acrylonitrile-N-phenylmaleimide copolymer, xcex1-methylstyrene-acrylonitrile copolymer, polymethyl methacrylate, methyl methacrylate-styrene copolymer, ABS resin, AAS resin, AES resin, polycarbonate, polyamide, polyester such as polyethylene terephthalate or polybutylene terephthalate, polyphenylene ether, known impact modifiers such as acrylic rubber-containing impact modifier, impact modifier containing acrylic-silicone composite rubber and butadiene rubber-containing impact modifier, and other known thermoplastic resins.
The silicone rubber particles are used in an amount of 0.1 to 100 parts by weight per 100 parts by weight of a thermoplastic resin. From the viewpoint of a balance of physical properties, preferably the amount is from 0.3 to 80 parts by weight per 100 parts by weight of a thermoplastic resin. If the amount is too small, no effect of the addition is obtained, and if the amount is too large, it is difficult to maintain the properties such as rigidity and surface hardness of the thermoplastic resins.
The graft copolymer particles are used in an amount of 1 to 150 parts by weight per 100 parts by weight of a thermoplastic resin. From the viewpoint of a balance of physical properties, preferably the amount is from 3 to 120 parts by weight per 100 parts by weight of a thermoplastic resin. If the amount is too small, no effect of the addition is obtained, and if the amount is too large, it is difficult to maintain the properties such as rigidity and surface hardness of the thermoplastic resins.
Also, the silicone rubber particles and the graft copolymer particles may be incorporated together into a thermoplastic resin. In that case, the amount of each of them may be selected within the above ranges.
Mixing of a thermoplastic resin with the silicone rubber powder and/or the graft copolymer powder isolated from the emulsions can be carried out by firstly mixing them through a Henschel mixer, a ribbon mixer or the like and then melt-kneading the mixture through a roll mill, an extruder, a kneader or the like.
The thermoplastic resin composition can also be obtained by mixing an emulsion of a thermoplastic resin with the silicone rubber emulsion and/or the graft copolymer emulsion and subjecting the mixed emulsion to coprecipitation of polymer particles.
The thermoplastic resin compositions of the present invention may contain conventionally used additives, e.g., plasticizer, stabilizer, lubricant, ultraviolet absorber, antioxidant, flame retardant, pigment, glass fiber, filler, high molecular processing aid and high molecular lubricant.
Molding methods conventionally used for thermoplastic resin compositions, e.g., injection molding, extrusion, blow molding and calendering, are applicable to the thermoplastic resin compositions of the present invention.
The obtained molded articles have excellent properties such as impact resistance, slipping property and flame resistance.
The present invention is more specifically explained by means of examples, but it is to be understood that the present invention is not limited to only these examples. In the examples, all parts and % excepting variation coefficient are by weight unless otherwise noted.
In the following examples and comparative examples, measurement and evaluation were made in the following manners.
[Polymerization Conversion]
Vinyl Monomer (a)
An aqueous emulsion of vinyl homo- or copolymer (A) was dried in a hot air dryer at 120xc2x0 C. for 1 hour to measure the content of solid matter of vinyl homo- or copolymer (A). The polymerization conversion was calculated according to the following equation.
[Solid matter content of vinyl polymer (A)/Amount of vinyl monomer (a) charged]xc3x97100 (% by weight)
Silicone Rubber-forming Component (b)
An aqueous emulsion containing silicone rubber particles was dried in a hot air dryer at 120xc2x0 C. for 1 hour to measure the content of solid matter of vinyl homo- or copolymer-containing silicone rubber. The polymerization conversion was calculated according to the following equation.
[Solid matter content of vinyl homo- or copolymer-containing silicone rubberxe2x88x92Solid matter content of vinyl polymer (A)/Amount of silicone rubber-forming component charged]xc3x97100 (% by weight)
[Average Particle Size]
Using a measuring apparatus, NICOMP MODEL 370 Particle Size Analyzer made by PACIFIC SCIENTIFIC CO., the number average particle size (xcexcm) and the variation coefficient in particle size distribution (standard deviation/number average particle size)(%) were measured by a dynamic light scattering method.
[Content of Toluene-insoluble Matter]
A vinyl polymer-containing silicone rubber obtained from an emulsion by drying it was immersed in toluene at room temperature for 24 hours, and was centrifuged at 12,000 r.p.m. for 60 minutes to measure the content (% by weight) of the toluene-insoluble matter in the vinyl polymer-containing silicone rubber.
[Izod Impact Strength]
The Izod impact strength was measured by using a notched xc2xc inch bar according to ASTM D-256. The testing temperature is 23xc2x0 C. unless otherwise noted.
[Falling Ball Impact Strength]
The test was made using a molded sheet having a size of 150xc3x97100xc3x972 (mm) prepared by injection molding, and the 50% failure energy at 23xc2x0 C. (falling ball weightxc3x97height) (kgxc2x7m) was calculated.
[Appearance of Molded Article]
The appearance of the molded sheet used in the evaluation of falling ball impact strength was visually observed and evaluated according to the following criteria.
∘: The surface state is good.
X: A black stripe patter is observed in the surface.
[Processability]
A resin composition was injected from an injection molding machine (model FAS100B made by Kabushiki Kaisha FUNAC) at a cylinder temperature of 250xc2x0 C. and an injection pressure of 1,350 kgf/cm2, and the flow length of the resin in a spiral mold having a thickness of 3 mm was measured.
[Slippability]
Using the molded sheet used in the evaluation of falling ball impact strength, the coefficient of dynamic friction was measured by a surface testing machine model HEIDON-14D made by Shinto Kagaku Kogyo Kabushiki Kaisha, wherein a molded sheet of polymethyl methacrylate having a size of 40xc3x9740xc3x973 (mm) was used as the opposite material and the test was made under a vertical load of 500 g at a sliding rate of 30 mm/minute.
[Flame Resistance]
Evaluation was made by UL94 V test using {fraction (1/12)} inch bar.
[Gloss]
The gloss was evaluated by 60xc2x0 light reflectance using a gloss meter model VG-10 made by Nippon Denshoku Kogyo Kabushiki Kaisha.